react-testing-standards（React 测试 standards）

React Testing Standards

Testing Philosophy

Guiding Principles

• Test user behavior, not implementation details
• Tests should resemble how users interact with your app
• Query by accessible roles and labels, not test IDs
• Integration tests over unit tests when practical
• Test the component contract, not internal state

What to Test

Priority High:

• User interactions (clicks, typing, navigation)
• Conditional rendering based on props/state
• API integration and data fetching
• Form submissions and validation
• Error states and error recovery

Priority Medium:

• Accessibility features
• Loading states
• Edge cases and boundary conditions

Avoid Testing:

• Implementation details (state variable names)
• Third-party library internals
• CSS styling (use visual regression tests)
• Framework behavior (React itself)

React Testing Library

Query Priority

1. Accessible Queries (Most Preferred):

• getByRole - Most preferred
• getByLabelText - For form elements
• getByPlaceholderText - Alternative for inputs
• getByText - For non-interactive elements
• getByDisplayValue - For current input values

2. Semantic Queries:

• getByAltText - For images
• getByTitle - For title attributes

3. Test IDs (Last Resort):

• getByTestId - Only when element has no accessible role

Query Variants

User Interactions

Library: Use @testing-library/user-event, not fireEvent

import { render, screen } from '@testing-library/react';
import userEvent from '@testing-library/user-event';

test('user can type in input', async () => {
  const user = userEvent.setup();
  render(<SearchBox />);

  const input = screen.getByRole('textbox');
  await user.type(input, 'Hello');

  expect(input).toHaveValue('Hello');
});

Common Interactions:

• user.click() - Click elements
• user.type() - Type in inputs
• user.clear() - Clear input values
• user.selectOptions() - Select dropdown options
• user.upload() - Upload files

Test Structure

Anatomy

import { render, screen, waitFor } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
import { ComponentName } from './ComponentName';

describe('ComponentName', () => {
  test('describes expected behavior', async () => {
    // Arrange - Set up test data and render
    const user = userEvent.setup();
    render(<ComponentName prop="value" />);

    // Act - Perform user interactions
    const button = screen.getByRole('button', { name: /click me/i });
    await user.click(button);

    // Assert - Verify expected outcomes
    expect(screen.getByText(/success/i)).toBeInTheDocument();
  });
});

Best Practices

• One logical assertion per test
• Descriptive test names (what behavior is tested)
• Arrange-Act-Assert pattern
• Avoid beforeEach for test setup (makes tests less clear)
• Use async/await for user interactions

Testing Patterns

Component Rendering

Basic:

test('renders with correct props', () => {
  render(<UserCard name="John" email="john@example.com" />);

  expect(screen.getByText('John')).toBeInTheDocument();
  expect(screen.getByText('john@example.com')).toBeInTheDocument();
});

Conditional:

test('shows loading state', () => {
  render(<DataDisplay isLoading={true} />);

  expect(screen.getByRole('progressbar')).toBeInTheDocument();
});

User Interactions

Button Click:

test('increments counter on click', async () => {
  const user = userEvent.setup();
  render(<Counter />);

  const button = screen.getByRole('button', { name: /increment/i });
  await user.click(button);

  expect(screen.getByText('Count: 1')).toBeInTheDocument();
});

Form Submission:

test('submits form with user data', async () => {
  const handleSubmit = jest.fn();
  const user = userEvent.setup();
  render(<LoginForm onSubmit={handleSubmit} />);

  await user.type(screen.getByLabelText(/email/i), 'user@example.com');
  await user.type(screen.getByLabelText(/password/i), 'password123');
  await user.click(screen.getByRole('button', { name: /submit/i }));

  expect(handleSubmit).toHaveBeenCalledWith({
    email: 'user@example.com',
    password: 'password123',
  });
});

Async Operations

Data Fetching:

test('displays fetched data', async () => {
  render(<UserList />);

  // Wait for loading to finish
  expect(screen.getByText(/loading/i)).toBeInTheDocument();

  // Wait for data to appear
  const users = await screen.findAllByRole('listitem');
  expect(users).toHaveLength(3);
});

With waitFor:

test('shows success message after submission', async () => {
  const user = userEvent.setup();
  render(<ContactForm />);

  await user.click(screen.getByRole('button', { name: /submit/i }));

  await waitFor(() => {
    expect(screen.getByText(/thank you/i)).toBeInTheDocument();
  });
});

Error Handling

test('displays error message on failure', async () => {
  // Mock API to return error
  jest.spyOn(api, 'fetchUser').mockRejectedValue(new Error('Failed'));

  render(<UserProfile userId="123" />);

  const errorMessage = await screen.findByText(/failed to load/i);
  expect(errorMessage).toBeInTheDocument();
});

Mocking

External Dependencies

API Calls:

// Mock API module
jest.mock('@/lib/api', () => ({
  fetchUsers: jest.fn(),
}));

test('renders users from API', async () => {
  const mockUsers = [{ id: 1, name: 'Alice' }];
  fetchUsers.mockResolvedValue(mockUsers);

  render(<UserList />);

  expect(await screen.findByText('Alice')).toBeInTheDocument();
});

React Query:

import { QueryClient, QueryClientProvider } from '@tanstack/react-query';

function renderWithQueryClient(ui: React.ReactElement) {
  const queryClient = new QueryClient({
    defaultOptions: {
      queries: { retry: false },
    },
  });

  return render(
    <QueryClientProvider client={queryClient}>
      {ui}
    </QueryClientProvider>
  );
}

What NOT to Mock

Avoid:

• React hooks (useState, useEffect, etc.)
• Component implementation details
• Child components (test integration instead)

Acceptable:

• External API calls
• Browser APIs (localStorage, fetch)
• Third-party libraries with side effects
• Date/time functions (Date.now())

Accessibility Testing

Practices

• Query by role (getByRole) enforces ARIA compliance
• Test keyboard navigation
• Verify focus management
• Check alt text on images

test('button is keyboard accessible', async () => {
  const user = userEvent.setup();
  render(<Dialog />);

  // Tab to button
  await user.tab();
  expect(screen.getByRole('button')).toHaveFocus();

  // Activate with Enter
  await user.keyboard('{Enter}');
  expect(screen.getByRole('dialog')).toBeInTheDocument();
});

Test Organization

File Structure

• ComponentName.test.tsx - Component tests
• utils.test.ts - Utility function tests
• __tests__/ directory - Alternative structure

Describe Blocks

describe('LoginForm', () => {
  describe('validation', () => {
    test('shows error for invalid email', () => {});
    test('shows error for short password', () => {});
  });

  describe('submission', () => {
    test('calls onSubmit with form data', () => {});
    test('shows success message after submit', () => {});
  });
});

Coverage Guidelines

Requirements

What to Prioritize

• User-facing features
• Business logic and calculations
• Error handling paths
• Form validation

Acceptable Gaps

• Pure presentation components
• Third-party library wrappers
• Type definitions

Common Pitfalls

Avoid

• Testing implementation details (state names, effect calls)
• Snapshot tests for everything (brittle and uninformative)
• Using getByTestId as primary query method
• Not awaiting async operations
• Asserting on intermediate loading states

Instead

• Test public API and user-visible behavior
• Snapshots only for static content that changes infrequently
• Query by role/label for accessibility
• Always await user events and async queries
• Assert on final rendered state

CI Integration

Requirements

• All tests must pass before merge
• Coverage reports generated and tracked
• Tests run on every pull request
• Fast test execution (< 5 minutes for unit/integration)